The present invention relates to an electrically controlled hydraulic actuating system. Although not exclusively, it is particularly suited to use on board aircraft, for controlling parts such as control surfaces for example.
Electrically controlled hydraulic actuating systems comprising:
a servocontrol, intended to control at least one moving part, such as a control surface, and comprising a cylinder inside which a piston to which said moving part is connected can move, said piston dividing said cylinder into two chambers, each of which is provided with a hydraulic connection port, and said servocontrol being provided with a control valve, for example of the servovalve or directly controlled valve type, connected to a hydraulic circuit in which a hydraulic fluid under pressure circulates;
a two-way hydraulic pump, driven in rotation by an electric motor driven by power electronics; and
a switching device allowing said hydraulic connection ports to be connected either to said control valve or to said pump,
are already known.
In these known systems, actuation of said moving part is, in normal operation, performed by said servocontrol supplied with hydraulic fluid by said circuit through said valve and said switching device. By contrast, in the event of failure of said hydraulic circuit or of said valve, the switching device connects said servocontrol to said hydraulic pump. Actuation of said moving part is then, under exceptional operating circumstances, the result of the servocontrol being powered by said pump driven by the electric motor, through the switching device.
As a result, these systems are generally known by the abbreviation EBHA which stands for electrical back-up hydraulic actuator.
Of course, both in normal operation (where the actuating system is being supplied from the hydraulic circuit) and in back-up operation (when the actuating system is being supplied from the pump and the electric motor), such known systems need to be able to provide the maximum performance needed to actuate said part. The result of this is therefore that, on the one hand, the hydraulic circuit needs to be designed for the maximum power of the actuating system and that, on the other hand, although used infrequently, said pump and its accessories need to be robustly engineered, which increases their cost and mass. Furthermore, for the very reason that they are little used, they may be the site of breakdowns that are difficult to detect.
The purpose of the present invention is to overcome these drawbacks. The invention relates to an electrically controlled hydraulic actuating system of the type recalled hereinabove in which the design not only of the pump and its accessories but also of the hydraulic circuit, the valve and their accessories can be scaled down, while at the same time making any breakdowns of the pump and of its accessories more visible.
To this end, according to the invention, the electrically controlled hydraulic actuating system, of the type mentioned hereinabove, is noteworthy in that said switching device is additionally able to connect said hydraulic connection ports of said chambers both to said control valve and to said pump, so as to allow said servocontrol to be supplied the sum of the hydraulic power delivered by said hydraulic circuit and of the hydraulic power, of electrical origin, generated by said pump actuated by said electric motor.
Such a system can therefore be termed electrically assisted hydraulic actuator, abbreviated to EAHA.
Thus, by virtue of the present invention, it is possible to provide maximum required performance by summing the hydraulic power and the electrical power available, the electrical power being used only during heavy demands for power likely to exceed the hydraulic capability. In other words, the hydraulic circuit and the control valve (which deliver the hydraulic power) are engineered to be able to perform most actuations, which require a power lower than that demanded for maximum performance. By contrast, the hydraulic pump and its accessories (which deliver power of electrical origin) are engineered to supply top-up power which, when added to said hydraulic power, allows said maximum performance to be provided. The result of this is that each element of the system according to the invention can be engineered according to the actual power (lower than the maximum power of said system) that it has to provide. In addition, because the xe2x80x9celectricalxe2x80x9d elements of the system, that is to say the motor, the pump and their air accessories, are called upon during operation of said system, their breakdowns cannot remain hidden.
In the system according to the present invention, said switching device may consist of a first and a second selectors with specific controls, it being possible for said first selector to be inserted between said valve and said connection ports, while the second selector may be arranged between the latter and said pump, and the specific controls of said first and second selectors allowing said hydraulic connection ports to be connected not only to said control valve or to said pump, but also to both said control valve and said pump.
As a preference, said first selector:
can adopt either a passing state or a non-passing state;
spontaneously adopts its non-passing state; and
is forced into its passing state by the action of the pressure of the hydraulic fluid of said hydraulic circuit, through a controlled electric valve.
Furthermore, according to a first embodiment, said second selector:
can adopt either a passing state or a non-passing state;
spontaneously adopts its non-passing state; and
is forced into its passing state by the action of a control device.
As an alternative, said second selector:
can adopt any one of three states, namely a passing state, a non-passing state or a passive state for which said second selector establishes external communication with restriction between said hydraulic connection ports;
spontaneously adopts said passive state;
is forced into its passing state by the action of a control device; and
is forced into its non-passing state by the action of the pressure of the hydraulic fluid of said hydraulic circuit, through said controlled electric valve.